A coating film including, as constituents, atoms of a metal such as aluminum and phosphorus atoms is conventionally known. For example, there is known an organic polymer formed product having a gas permeation-preventing coating film made of a metal orthophosphate whose main constituent is aluminum (Patent Literature 1: JP 55(1980)-46969 A). JP 55(1980)-46969 A discloses a method for forming a gas permeation-preventing coating film by applying a dispersion liquid or a solution of a metal orthophosphate to an organic polymer formed product. JP 55(1980)-46969 A discloses a method for forming a dispersion liquid or a solution of a metal orthophosphate, the method consisting of respectively dissolving an aluminum ion source and a phosphorus ion source in separate media, and then mixing the resultant solutions together.
There is also known a layered film with gas barrier properties in which an inorganic oxide-deposited layer is provided on a base film formed of a plastic film, and a coating layer of a metal phosphate is provided on the inorganic oxide-deposited layer (Patent Literature 2: JP 2006-116737 A). JP 2006-116737 A discloses a method for forming a coating layer of a metal phosphate, the method consisting of applying a particular coating liquid obtained by mixing of a phosphate ion-containing solution and a metal ion-containing solution.
There is also known a method using aluminophosphate in order to reduce the surface roughness of a base made of iron, glass, or the like (see Patent Literature 3: JP 2006-515535 T). JP 2006-515535 T discloses a method for forming an amorphous aluminophosphate compound on a base made of iron, glass or the like by applying onto the base an aluminophosphate compound precursor including aluminum ions and a phosphoric acid ester in a liquid medium.
Furthermore, there is known a composite body composed of: a base made of metal, metal alloy, plastic or the like; and a coating component including a particular aluminum phosphate compound (see Patent Literature 4: JP 2008-516015 T). JP 2008-516015 T discloses a method for forming a coating using a solution including an aluminum salt and a phosphoric acid ester in an organic solvent.